1. Field of the Invention
This invention relates to the art of manufacturing flat glass, wherein molten glass is delivered onto a surface of a pool of molten metal and formed while floating on the molten metal into a continuous sheet of glass. More particularly, this invention relates to improved dam barriers positioned in the glass-supporting molten metal to control convection currents or flow of molten metal within the pool.
2. Brief Description of the Prior Art
The use of dam barriers to influence thermal conditions within a glass-supporting pool of molten metal in a glass forming chamber has long been recognized. For example, U.S. Pat. No. 789,911 to Hitchcock discloses the use of a plurality of barriers to segregate a glass-supporting pool of molten metal into a plurality of pool segments, each of which may be selectively maintained at a desired temperature to permit the cooling and forming of glass as it passes over each segment of the pool during its travel through a forming chamber.
U.S. Pat. No. 3,317,302 to Misson discloses the use of dam barriers which are sufficiently beneath the glass-supporting surface of a pool of molten metal so that, while segregating the pool into several segments, they permit the flow of molten metal along the length of the forming chamber to a desired degree to effect the cooling of the glass during its formation.
U.S. Pat. No. 3,584,475 to Galey and Sensi discloses dam barriers extending transversely across the bottom of a glass forming chamber which are contoured to provide for a greater inhibition of molten metal flow along the margins of a forming chamber than in the central portion of the forming chamber.
U.S. Pat. No. 3,930,829 to Sensi discloses the use of dam barriers in a forming chamber, some of which are positioned inwardly from the side walls of the forming chamber so that the flow of molten metal along the extreme marginal portions of the forming chamber is not inhibited by the presence of a dam barrier while the flow of molten metal throughout a major central portion of the forming chamber is inhibited by the presence of the dam barriers. In this patent, Sensi also discloses the use of short dam barriers which do not extend across the full width of a forming chamber such as dam barriers 280 shown in FIG. 14 of U.S. Pat. No. 3,930,829. It is recognized that these dam barriers alone would locally inhibit the flow of molten metal in the pool of molten metal while permitting the flow of molten metal in both a central portion of the pool and in marginal portions of the pool beyond the barriers 280.
Modeling of glass forming processes has indicated that some short circuiting of molten metal flow over submerged dam barriers results in a fast flow of molten metal along with the advance of glass along its surface immediately adjacent the interface between the glass and the molten metal. This flow appears to reduce the effectiveness of submerged dam barriers. The present invention is therefore directed to an improved method and apparatus for the control of molten metal flows within the glass-supporting pool of molten metal.